Modern power generating stations or power plants use steam turbines to generate power. In a conventional power plant, steam generated in a boiler is fed to a turbine where the steam expands as it turns the turbine to generate work to create electricity. Occasional maintenance and repair of the turbine system is required. When the turbine is taken out of service, it is typically more economical to continue boiler operation rather than shutting the boiler down during turbine repair. To accommodate this, the power plant is commonly designed with supplemental piping and valves that circumvent the steam turbine and redirect the steam to a recovery circuit that reclaims the steam for further use. The supplemental piping is conventionally known as a turbine bypass circuit.
When the turbine bypass circuit is in operation, steam that is routed away from the turbine must be recovered or returned to water. To return the steam to water, a system must be designed to remove the heat of vaporization from the steam, thereby forcing it to condense. An air-cooled condenser is often used to recover steam from both the turbine bypass circuit and the steam exhausted from the turbine. The air-cooled condenser facilitates heat removal by forcing low temperature air across a heat exchanger in which the steam circulates. The residual heat is transferred from the steam through the heat exchanger directly to the surrounding atmosphere.
Typical air-cooled condensers have temperature and pressure limits. Because the steam from the turbine bypass circuit or bypass steam has not produced work through the turbine, its pressure and temperature is greater than the turbine-exhausted steam. As a result, the higher temperature and pressure of the bypass steam must be conditioned or reduced prior to entering the air-cooled condenser to avoid damage to the condenser. Cooling water is typically injected into the bypass steam to moderate the steam's temperature. To control the bypass steam's pressure prior to entering the condenser, control valves, and more specifically, fluid pressure reduction devices, commonly referred to as spargers, are used. The spargers are restrictive devices that reduce fluid pressure by transferring and absorbing fluid energy contained in the bypass steam. Typical spargers are constructed of a cylindrical, hollow housing or a perforated tube that protrudes into the turbine exhaust duct. The bypass steam is received in the hollow housing and transferred by the sparger into the duct through a multitude of fluid passageways to the exterior surface. By dividing the incoming fluid into progressively smaller, high velocity fluid jets, the sparger reduces the flow and the pressure of the incoming bypass steam and any residual cooling water within acceptable levels prior to entering the air-cooled condenser.
In power plants with multiple steam generators, multiple spargers are mounted into the turbine exhaust duct. Because of space limitations within the duct, the spargers are generally spaced very closely and may impede the flow of exhaust steam from the steam turbine into the air-cooled condenser. Steam turbines are designed to exhaust into a specific back-pressure within the turbine exhaust duct to optimize their operation. The back-pressure within the turbine exhaust duct is directly related to the aerodynamic resistance or drag presented by the spargers. Conventional spargers used in modern power plants do not minimize the drag within the duct and subsequently can reduce the efficiency and output of turbine.
Applications with conventional spargers may not only limit turbine performance, but can also impact the expense and design of the air-cooled condenser. For example, the number of turbines used in the power plant determine the size and volume of the air-cooled condenser, including the available area to mount the spargers within the turbine exhaust duct. Back-pressure restrictions introduced by the conventional spargers in the condenser circuit limit the total heat reduction the bypass steam that can be achieved thereby increasing the size and cost of the entire air-cooled condenser system.